1. Field of the Invention
The present invention relates to controlled release fertilizers and particularly to fertilizer-pesticide compositions. The invention is more particularly directed to fertilizers and fertilizer-pesticide compositions to which thin or ultrathin films or coatings of sulfonated polymers have been applied as an improved controlled release agent. Related to this, the present invention is directed to methods for producing fertilizer and fertilizer-pesticide composites coated with sulfonated polymers in addition to agricultural processes involving the use of such coated fertilizers and fertilizer-pesticide composites. In this regard, agricultural processes in which the fertilizer and fertilizer-pesticide composites coated with sulfonated polymers in accordance with the present invention may be applied include processes for enhancing vegetation including plant growth stimulation and regulation as well as stimulation of seed germination.
2. Discussion of Background and Material Information
Carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur are the primary elements essential to plant growth. Soils contain all of these elements in addition to other macro and micronutrients that enhance plant growth. Typically, however, such elements are seldom present in the soil in sufficient quantity or in forms that can support maximum plant productivity and yield. Therefore, fertilizers having specific chemical formulations and in pre-determined amounts must be added to enrich the soil to ensure maximum plant yield. The amount and form of the fertilizer added are pre-determined by chemically assaying the amount and availability of the required nutrient(s) in the soil, for example, as disclosed by Methods of Soil Analysis. 1982. Amer. Soc. Agronomy, Madison, Wisc. Thus, appropriate fertilizer is added in amounts calculated to ensure the required plant yield based on known fertilizer response curves established by extensive agronomic testing for the particular plant and plant growth environment.
Fertilizers containing nitrogen, phosphorus, sulphur and/or potassium, by way of example, may be applied as solid granules or in liquid form. These primary fertilizers may be supplemented with certain trace elements such as copper, iron, manganese, zinc, cobalt, molybdenum, boron usually supplied as oxides or salts containing the elements in the cationic form. Suitable salts are, for example, sulphates, nitrates, chlorides, molybdates or borates. The difference between trace element deficiency and toxicity, however, is but a few parts per million as measured by the concentration of the element in the soil. Moreover, the efficiency of utilization of fertilizers, i.e., the percent uptake of the applied fertilizers is notoriously low. In this regard, chemical, biological and physical processes compete with the plant for the added fertilizer nutrients usually to the detriment of plant productivity. In addition, nitrogen fertilizers added to the soil may be leached into groundwaters, chemically immobilized into clay minerals, chemically removed by volatilization of ammonia, biologically removed from the soil by denitrification to dinitrogen and nitrous oxide gases or immobilized into the active microbial biomass. These competing and simultaneous occurrances result in fertilizer use efficiency of nitrogen often being less than 50%. Thus, when 100 kg N/ha is added to the soil, the plant actually "sees" only 50 kg N/ha. Although most soils contain high levels of phosphorus, it is chemically immobilized as calcium phosphates, e.g. in soils of pH &gt;7.0 or iron and aluminum phosphates, e.g. in soils of pH &lt;5.0, and is thus not plant-available. Fertilizer phosphorus applied to these soils, however, is rapidly immobilized resulting in fertilizer use efficiencies seldom exceeding 30%.
If the release of nutrients from fertilizers could be controlled to more closely match the actual physiological requirements of the plant for the nutrient and if temporary or permanent losses of the fertilizer nutrients could be minimized if not eliminated, several advantages would accrue:
i) less fertilizer would be required to achieve the same plant yield, PA1 ii) the same amount of fertilizer could be applied resulting in higher yields and concomitant lower per unit plant production costs; PA1 iii) less water-soluble nitrogen would leach into groundwaters thus minimizing ground-water pollution; and/or PA1 iv) less nitrogenous gases would evolve into the atmosphere thus minimizing damage to the fragile ozone layer.
Although it is known to protect solid substrates, such as pipes, slabs, sheets and the like from the external environment with the use of barrier or protective coating materials, this technology has not been applied in accordance with the present invention, particularly with respect to agricultural products. In conventional applications, however, polymers or other organic materials are widely used as coatings to provide protection from water or moisture. For cost effectiveness these materials are typically applied as thin films. The thickness of the film depends upon the desired degree of water protection. The thicker the film, the more likely that water penetration would be slowed down. In practice, applying an effective thin coating is difficult because of the various stresses tending to make the film discontinuous (e.g., film-rupture, pin holes). Films will rupture when a threshold stress is exceeded. The lateral stress tending to rupture a film is inversely proportional to an exponential power of the film thickness. The thinner the film, the more easily it will rupture. To provide film strength current practice requires the establishment of crosslinks in the coating by curing. Crosslinking, i.e. curing, can also improve the coating's resistance to water. Thin films which consist of molecules in relatively random configurations with a high degree of entanglements are superior to films containing molecules in relatively coiled states with few molecular entanglements. Accordingly, polymers containing associating ionic groups, i.e. ionomers, which have a high degree of molecular interactions make excellent protective films.
There are many applications for thickened or gelled solutions of polymers in inorganic liquids. There are also a number of physical and chemical techniques for preparing such systems. The present invention, however, is concerned with polymeric coatings having improved properties which have been found to be particularly suitable for application to agricultural products, such as fertilizers, pesticides, herbicides, insecticides, bacteriocides, fungicides, nematicide, sporicides, and the like, in addition to combinations thereof.